A thick crustal block revealed by reconstructions of early Mars highlands

Sylvain Bouley (1, 2) , James Tuttle Keane (3) , David Baratoux (4) , Benoit Langlais (5) , Isamu Matsuyama (6) , F. Costard (1) , Roger Hewins (7) , Valérie Payré (8) , Violaine Sautter (7) , Antoine Séjourné (1) , Olivier Vanderhaeghe (4) , Brigitte Zanda (2, 7)

1 GEOPS - Géosciences Paris Saclay
2 IMCCE - Institut de Mécanique Céleste et de Calcul des Ephémérides
3 CALTECH - California Institute of Technology
4 GET - Géosciences Environnement Toulouse
5 LPG - Laboratoire de Planétologie et Géodynamique [UMR 6112]
6 LPL - Lunar and Planetary Laboratory [Tucson]
7 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
8 Rice University [Houston]

The global-scale crustal structure of Mars is shaped by impact basins, volcanic provinces, and a hemispheric dichotomy with a thin crust beneath the northern lowlands and a thick crust beneath the southern highlands. The southern highlands are commonly treated as a coherent terrain of ancient crust with a common origin and shared geologic history, plausibly originating from a giant impact(s) or a hemispheric-scale mantle upwelling. Previous studies have quantified the contribution of volcanism to this crustal structure; however, the influence of large impacts remains unclear. Here we present reconstructions of the past crustal thickness of Mars (about 4.2 Gyr ago) where the four largest impact basins (Hellas, Argyre, Isidis and Utopia) are removed, assuming mass conservation, as well as the main volcanic provinces of Tharsis and Elysium. Our reconstruction shows more subdued crustal thickness variations than at present, although the crustal dichotomy persists. However, our reconstruction reveals a region of discontinuous patches of thick crust in the southern highlands associated with magnetic and geochemical anomalies. This region, corresponding to Terra Cimmeria–Sirenum, is interpreted as a discrete crustal block. Our findings suggest that the southern highlands are composed of several crustal blocks with different geological histories. Such a complex architecture of the southern highlands is not explained by existing scenarios for crustal formation and evolution. A discrete block of thick ancient crust revealed by a crustal reconstruction suggests a complex geologic history for the southern highlands of Mars.

Domaines: Planète et Univers [physics]; Sciences de la Terre; Physique [physics]; Astrophysique [astro-ph]

Sylvain Bouley, James Tuttle Keane, David Baratoux, Benoit Langlais, Isamu Matsuyama, et al.. A thick crustal block revealed by reconstructions of early Mars highlands. Nature Geoscience, 2020, 13 (2), pp.105-109. ⟨10.1038/s41561-019-0512-6⟩. ⟨hal-02900960⟩